This forum is wonderful and I'm seeing lots of people dipping their toe into the world of modding for the first time with lots of enthusiasm but the most common problem I see that people are having with their projects is that probably 70% of the problems you guys are encountering are solvable by improving your soldering technique, So I'm taking it upon myself to share my >30 years of soldering experience with you all (I'm ~40 and yes, that means I was soldering when I was 8~9! I studied Electronic engineering at university and though I actually went into software/programming as a career, I have been a hobbyist electronic tinkerer in all of that time too.)

so with that into out of the way, lets start with the guide!
Firstly the unfortunately essential... WARNING:(borrowed from @sotasystems )First of all, I want to tell you that whatever you do following this guide, you do on your own risk. As we are in the age where people like to think that they can offload their own responsibilities onto other people, I feel I should point out that, should you choose to follow this guide on your own hardware/software, it is your own responsibility when something goes wrong in any way and you are entirely on your own.
Soldering is a skill that needs practice. Followed by more practice then finally some more practice.
But this isn't The Simpsons and your guidance won't be just 'tappa tappa tappa'. Tl;Dr version:
Practice first before doing your GBZ
get this stuff:

Soldering iron > $30 Antex or weller

spare/alternative tips

stand

wire sponge for cleaning

helping hands

63:37 solder (or RoHS leadfree solder if you must )

flux

desoldering braid/sucker

pliers, wire cutters, tweezers

</Tl;Dr version>Rule 0 - Practice first before diving into your heartfelt project
I see this in all the computing communities I'm in. when you get the idea to start a project, the enthusiasm takes over and you just want get cracking with it and get [your project] made by the end of the weekend!
BUT! Soldering is a learned skill. Nobody is good at it out of the box. you don't expect to be able to paint like Michaelangelo on your first painting, and soldering is no different (ok it is easier than becoming a master painter but when you first pick up the iron it's just as terrifying)
It's heartbreaking spending a ton of money on parts only to then destroy them because you also used the expensive parts to PRACTICE on by diving straight in.
While getting hold of one of the many AIO boards it taking a SUBSTANTIAL amount of work out of the project, you don't want to then let it down by doing a crappy job hooking it all up, or worse still, destroying the work done by @Helder or @kite (or maybe me... who knows, watch this space ) especially if the board is in short supply, meaning you may not be able to get a replacement for a long time, if ever...
So with that, I'm going to give you some nice easy soldering exercises that you can do to get your skill up enough to actually confidently turn your hand to your shiny AIO or PiZer0.

Part 1 - Stuff
You don't need ALL of this stuff, but this is the minimum level you should have to be able to cope with 90% of situations.

* Soldering Iron - well duh!

soldering ironShow

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There are soldering irons and there are soldering irons. this morning I read a thread where someone's cheapo iron had melted on them. That's right, someone couldn't design a soldering iron that was even able to function as a soldering iron!
you don't need to spend uberbucks on one unless you plan to do go into component level replacement as a profession, but try to avoid $10 ones.
also don't be tempted to use a "soldering gun"

avoid these like the plagueShow

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They have no precision and deliver way too much heat in a fairly uncontrollable manner. They're good for soldering household wiring, but not a great deal else, certainly not fine pitch electronics!

good brands are weller and antex and reasonable ones are going to cost £/$30 and up.
optionally if you have the budget, go for a temp controlled one like this weller:

temperature controlled wellerShow

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at the very least try and get one with interchangeable tips, so that you can replace them when they become unusable and swap them for different shapes for different tasks, which brings me to...

* Tips
Not the kind you might give to a restaurant server but replacement ends for your iron

just the tipsShow

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Chances are your iron will come with a pointy or a chisel tip but as you get better at soldering, you'll want to make use of different tips for different tasks. Blunt points and flat chisel styles will be good for most general uses but fine points, knife edge, and round chisel shapes will make doing finer work like SMD not only easier, but actually possible.

* Stand

basic standShow

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Some irons come with a stand (usually "stations"), some do not. get one. end of.
there's nothing worse than trying to balance a hot iron on your kitchen table while holding your solder in one hand, PCB in another, component in another and wire in another, only to knock the iron off the table with your elbow and burn a hole in the vinyl flooring... not that I've ever done that. nope.
most stands come with a little tray and a sponge. keep the sponge wet, and clean the iron tip on it. constantly
an optional upgrade is to use a pot of wire sponge like this:

Seriously, this stuff is amazing, I don't know how I ever soldered before I had this in my life. wet sponge cleans the tip, kinda-okay-ish where the wire makes the tip brilliant every time. I say it's optional but it's so cheap, just get some.

* Helping hands

classic handsShow

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did you count how many hands I mentioned when I "dropped" the iron on the floor?
this is how you get 4 hands... totally indispensable.
The ones above are the traditional, cheap and abundant (and sometimes slightly useless!) version but more modern hands use these cooling pipes as the arms:

* Solder - again duh.
So I'm going to stick my neck out and say get 63:37 leaded solder. yes lead. yadda yadda. but you're not making things on an industrial scale. your environmental impact from making a few hobby projects is not even noise. also it you're working on a PCB from a DMG... guess what! yeah it's all done with 63:37, and RoHS solder doesn't really play well with 63:37
Also it's easier to work with, just make sure your environment is ventilated. I'm up-playing the risk here just because people will inevitably say "BUT LEAD!" so set up an extraction fan if it worries you. just a small 80mm PC fan will do the trick, just have it suck away from you.
If it really worries you just use RoHS but still have extraction, as the smoke that comes from soldering is the rosin flux burning off and it's not a great thing to be inhaling.

* Flux
Not a capacitor...
There's a little flux in your solder but sometimes you just need more.
can be bought in dispensing pens as liquid or as paste in cans. not to be confused with plumbing flux though. make sure it's for electronics. other than that just get whatever they have at Maplins(if you're in the UK -ebay and amazon are now your best bets unless you happen to have a local hobby shop nearby. Is Radio Shack still a thing in America?) once you've practiced a bit you might develop a preference for a specific type/brand.

because accidents happen and sometimes you need to undo your solder joint and get a bunch of things out of holes that you soldered together
goes well with it's de-soldering partner in crime:

* solder sucker

suckaShow

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not to be confused with Austin Powers' Sweedish pump...
literally sucks molten solder out of your joint...
both the wick and sucker are optional, but when you're a beginner you make a lot of mistakes and these will help you rectify them

* other bits

Pliers - regular and needlenose tipped

Wire cutters - preferebly flush cutting

Fine Tweezers - more important for SMD work but still useful for holding components in place

Ok that's the basics (!) but with that you tackle almost any job going and to get the final 10% you're going to need some pretty expensive bits of kit, whereas this lot will all fit into a small tool wallet and is usually available as a whole set (soldering starter kit etc)

I've typed enough for now, look out for part 2 where I get into actual soldering

Last edited by abrugsch on Fri Dec 07, 2018 4:26 am, edited 15 times in total.

Part 2 - Theory, Technique and Practice
So now you have all the hardware you need to do a good job (or don't worry if you don't have everything, you don't need it all to get practicing) lets take a look at what soldering actually is.
(note - in the interests of getting this guide done, I'll be using images from adafruit under CC BY-SA 3.0, just until I can shoot some of my own)

Good JointsShow

Perfect joint

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Good Heat
In it's simplest explanation, soldering is the melting of a metal alloy that has a relatively low melting point in between 2 other metals that have a much higher melting point. When the solder freezes, it bonds the two metals together with high electrical conductivity.
In order for this to happen, the solder must be above it's melting point, and the target materials must also be sufficiently hot to allow the melted solder to "flow" into the gaps and form the correct bond to the solder. If the target isn't hot enough the solder won't bond properly and you get a "Dry" or "Cold" joint. These are both not mechanically sound and will break apart over time nor electrically great. Fortunately for us good and bad joints are trivially easy to spot once you know the tells, and mostly easy enough to fix.

Flux
So the key thing of a good solder joint is heat right? If everything is hot enough that's all that's important right?
Well heat is important but not the end of the story. The bond surfaces also have to be clean otherwise the solder won't flow. This doesn't mean you need to scrub your components and PCB's before you use them (though sometimes you might need to remove severe oxidisation with a light abrasive such as a fibreglass pencil) But this is where the magic of flux comes in. As mentioned in part one, most reel solder comes with flux built in which melts with the solder. The melted flux then flows faster than the solder into all the channels and cleans as it goes, providing a platform for the solder to bond to. HOWEVER, the flux is only good for a couple of seconds before it burns away completely.

Bad Heat
Therefore heat is also Enemy number 1 though. Excessive heat damages components, insulation and the PCB itself. Any component that has more complexity than a resistor will be damaged by too much heat exposure, and if the insulation on connecting wires melts, it can pull away from the wire leaving it exposed and liable to making contact with other wires or components and shorting them. At best you get signals crossed, at worst you fry components wrong voltages or high currents. And the bond holding the PCB trace to the board itself can only withstand a certain amount of heat before it lets go and you get a trace lifting or weakening, leading to tearing and nothing to solder to.
The two biggest culprits are having an iron set too hot, and over-working the joint for too long. In the case of over-working, you should try not to have your iron in contact for more than about 10 seconds (and even that is pushing it...) your joints should really take no more than 3-5 seconds. (Literally get the iron onto the joint, add solder and pull out while everything is flowing. For 90% of typical through hole joints (resistors, pins etc.) it's easy as 1...2...3. 1:iron in. 2:solder in. 3:pull out. Typical exceptions to this are large components with big heat dissipaters (heatsinks, casings) or heavy circuit board tracks like power and ground planes. This is where a good temperature controlled iron or higher wattage come in so you can either dial in the higher temperature or have enough wattage to not have all your iron's heat drawn away by the component/plane.

Technique:
So I mentioned briefly above about thinking 1,2,3. Think this through first and try with a cold iron for initial practice. If you're doing this with a cold iron, then skip step 0, otherwise
Step 0: tin the iron.

Nicely Tinned TipShow

tinning

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Always make sure the tip is clean and shiny by adding a dab of solder to the tip, then clean it off immediately on your wet sponge pad or in your wire mesh right before doing your joint.

Always clean the tipShow

wet sponge or wire mesh to clean the tip

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If you are struggling to get the tip shiny, you may need to resort to some tip cleaner/conditioner. If you've left it a minute or two between tinning and doing the joint, then do it again. The burnt flux residue will hamper your efforts at getting a good joint. As an extra measure add another dab of solder onto the tip, literally the smallest amount you can get away with. this will give you more surface area for heat transfer for step 1. Use helping hands or other clamp/vice to keep the components steady. Even blu tak or painters tape work well. Movement of parts during the cooling process will prevent a good joint forming.

Step 1, Heat.

Heat the JointShow

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Put the iron's tip onto the joint so it's making contact with the component leg and the solder pad it's connecting to. You're needing to get heat into both to make sure the solder bonds correctly, so make sure it's touching both parts. this will take practice to get right for your iron's tip but once you 'get' it, it becomes second nature. You want to aim for this to be around a second or two but bigger components might take a little longer. if you have a component that really sucks heat out it's usually better to heat that first and only heat the PCB pad when the component is heated up to avoid trace damage.

Step 2, add in the Solder.

Insert SolderShow

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How much depends on the thickness of the solder and the size of the parts you're soldering, but again a guideline is to push it in for about a second. Push it at your components and joint, not the iron tip and it should now start flowing into the joint. It doesn't matter if it gets on the tip but there should be enough heat in the joint that it's not needed. if it's not melting and flowing, then try and touch the solder to the tip to initiate the flowing process. If it doesn't flow nicely into the joint by now then you probably don't have enough heat for that joint. You want to get enough solder in that it flows around the base of the pad, into the PCB hole (if it's through plated) and a little up onto the leg. The aim is to make a little tent shape between the pin/leg and the pad.

Step 3, Pull out!

Pull the tip outShow

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While the solder is still flowing and the flux is spitting and bubbling, pull both the solder and the iron off the joint, with maybe a slight lead on the solder just fractionally before the iron. Basically as soon as there's enough solder to make the tent, pull out. While it's cooling don't disturb the board or components. If all has gone well you should have a nice shiny tent shape covering the whole base of the pad and all the way around the leg/pin.
Common bad joints look like this:

Bad JointsShow

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If all is good, you can tidy up the joint by trimming any excess lead/wire. You want no more than 1mm above the top of the joint, but preferably cut the excess down to the top of the 'tent' with your wire cutters. if you're soldering a chip or socket or a row of header pins then you generally don't need to trim.

Indications that you've spent too long on the joint:
Burned flux: The flux residue of a good joint should be a light to mid amber colour if it's tending towards dark brown or black then it's probably gone too far and burnt flux has the opposite effect of fresh flux and hinders soldering. Either start again afresh if it's a practice piece or attempt to re-do it later (recovering mistakes will be later in the guide).
Pointy jaggy peaks: after you pull the iron away some of the solder clings to the iron tip and pulls a jaggy peak off the joint. this means all your flux burned away before you were done and the joint may be dry/cold.
Lifted track/pad: you've spent way too long with too hot an iron and have burned the bond between the trace and the board and the pad has lifted.
Fixes for these will be covered in Part 3.

So to recap: iron should be hot enough for the task. For simple through hole resistor pins, then a fixed temp ~25W iron will be fine. on a temp controlled iron, set 280-300 degrees C. Only go above this if you're really struggling with a particular joint due to reasons mentioned above. If absolutely nothing is orking, try incrementing by 10 and trying again.

0. Tin and clean the tip. (get in the habit of doing this frequently)
1. heat the joint 1-2 seconds
2. push solder in to the joint (not the iron) push solder in for ~1 second
3. Get Out!

1.2.3.

1.Iron in 2. Solder in 3. GET OUT!
Done in 3 seconds

Practice!
you'll need:
some perfboard

PerfboardShow

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some random components. resistors and LED's are cheap, but ideally a bag of random components can usually be bought from ebay/amazon cheaply, also maplin stores in UK usually have random bags available, and I'd guess your countries equivalent electronics store (Radio shack?) probably does too.
some single row header pins.

So for practice, get your perfboard and stick any of the components through and solder them in place.

ComponentsShow

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As this is just practice, it doesn't matter what goes where or how, just stick any 10 things through, and set the board up to not move (helping hands, vice, tak... doesn't matter just get it stuck.)

solder them all using 1.2.3. then do another 10 components. 1.2.3. 1.2.3.
once you start getting joints done nicely (with shiny tents) in around 5 seconds, then move on to header pins.

Set up a string of header pins about 10 long into your perf board. Solder each of the pins down. The challenge here being that all the pins are in close proximity to each other (0.1" to be precice) and you have to get your iron in around the other pins. When I've done soldering workshops with people who are learning to solder, it was the large numbers of header pins whcih saw the biggest increase in competance. by the time you've done 20-30 resistors and 20 or so header pins you you should be ready to take on the project kit that you ordered above. Once you've made that up, if you've been concentrating on technique you should be able to solder through-hole like a pro! you have a target time of 3 seconds per joint, but don't worry if for a wile it takes longer, just as long as you're getting consistent shiny tents.

Whew...
Ok sorry this one took so long, the next part shouldn't take anywhere near as long, so keep an eye out for part 3, fixing mistakes.

Last edited by abrugsch on Thu Apr 20, 2017 4:53 am, edited 3 times in total.

Thanks!
I've seen just a few too many things scattered around that just started to make me a bit sad. So I figured that while there are *loads* of guides already out there, you need to hunt out good ones and it's clear there are a few people who haven't done that.

Nice guide! I can't tell you how many people have told me pads came off or the solder won't stick (because the pad is gone!). Turns out their cheap soldering iron is too hot and because of inexperience they held it too long in place while melting the solder.

I personally like 63/37 fine solder for my work, 60/40 seems to give dull joints as seen in many builds and is often hard to tell if it's melted. I also assume this is another reason people keep their irons on a particular pad because it doesn't look like it has melted.

People mess up this way and assume I'll just exchange it for a new board and I have to tell them no because the damage is their fault. So I hope new soldering enthusiasts follow the guide you made so everyone is happy in the end.

Interesting point about the difference between 60:40 and 63:37. I was just using 60:40 as shorthand for leaded vs leadfree but if that slight difference in the ratio makes a big difference to the results (have to say I've probably actually been using 63:37) then I'll change it above.

I was actually hoping to do part 2 of the guide tonight while down at my hackerspace but just as I was getting ready I started to feel unwell so hopefully tomorrow, though I might do a bit with borrowed pictures at lunchtime

As a scrub I found the solder sucker to be the far better, albeit more expensive, option. I still have garbage cheap ass soldering irons which work well enough but would still rather have spent money on a solid brand. The cost of tools for this project are not cheap if you're starting with nothing, but that doesn't mean you should cheap out on them either if you're able.

Ganreizu wrote:As a scrub I found the solder sucker to be the far better, albeit more expensive, option.

I love them but find braid to be a required companion.

I still have garbage cheap ass soldering irons which work well enough but would still rather have spent money on a solid brand. The cost of tools for this project are not cheap if you're starting with nothing, but that doesn't mean you should cheap out on them either if you're able.